Wide band, short wave antenna and transmission line system



P. S. CARTER Dec. 5, 19-39.

WIDE BAND, SHORT WAVE ANTENNA AND TRANSMISSION LINE SYSTEM Filed Feb. 15, 1938 INVENTOR. PH /P s. CARTER BY 7% f ATTORNEY.

Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE Philip S. Carter, Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 15, 1938, Serial No. 190,555

2 Claims.

The present invention relates to short wave antenna and transmission line systems, for providing a substantially flat impedance versus frequency characteristic over a wide range of frequencies, such as may be encountered in television transmission or reception. More particularly, the present invention relates to improvements in short wave antenna and transmission line systems of the type described in my copending applications, Serial Nos. 147,817, filed June 12, 1937; 187,594, filed January 29, 1938; 188,821, filed February 5, 1938; and 190,939; filed February 17, 1938. In brief, the antennas described in my copending applications comprise conductive structures in the form of one or more conical surfaces of revolution having transmission line feeders connected to the apices thereof.

In my above-mentioned 'copending applications, the short wave antennas per se consist of conical surfaces of revolution to whose apices the transmission line feeders are connected. Since the field configuration between any two conical surfaces of revolution of the type described in these applications corresponds to a spherical wave expanding from the apices of the cones out to the large ends thereof, and since the field configuration in an ordinary transmission line corresponds to a plain wave, it will be evident that at the junction points of the transmission line and the conical antennas (i. e., their apices) there will be an abrupt change of field configuration from that corresponding to a plain wave to that corresponding to a spherical wave, and vice versa, depending upon whether the antenna and transmission line is used as a transmitter or a receiver.

One of the objects of the present invention is to avoid the abrupt changes in the electromagnetic field configuration between the transmission line and the short wave antenna of the type described in my copending applications.

In order to overcome this abrupt change in field configuration between the transmission line feeder and the conical surface of revolution, I propose to taper my antenna, which is in the form of a conical surface of revolution, Very gradually until the apex of the cone joins with and has the same dimensions as the transmission line to which it is connected. Putting it another way, I propose to gradually increase the dimensions of the transmission line until it forms part of and has the same dimensions as the conical surface of revolution (antenna) to which it is joined.

According to one embodiment of my invention, the dimensions of the transmission line are gradually increased, and the directions of the transmission line conductors changed near the points of junction with the conical surfaces of revolution. In this way, where a short wave an locations of increase in dimensions of the inner I conductor, over some distance, so that in effect the outerconductor has a wide mouth at the point of termination adjacent the antenna. The increase in dimensions of the outer conductor may or may not be in proportion to the increase in dimensions of the inner conductor. In accordance with a particular embodiment of the invention, the coaxial transmission line has the outer conductor tapered in the form of a horn. Where two separate coaxial lines are employed to feed energy to or receive energy from a pair of opposed conical antenna structures, the outer conductors of said two lines may take the form of horns extending in opposite directions.

A better understanding of the invention may be had by referring to the following description, which is accompanied by a drawing, wherein:

Fig. 1 illustrates one embodiment of my invention having a transmission line in the form of two open parallel conductors connected to my short wave antenna Fig. 2 illustrates another embodiment of my invention, wherein a coaxial type of line connects with a single conical antenna structure; and

Fig. 3 illustrates a third embodiment of my invention, wherein a pair of conical antenna structures are connected to a pair of coaxial transmission lines, in accordance with the invention.

Referring to Fig. 1, there is shown a short wave antenna and transmission line system providing a substantially fiat impedance versus frequency characteristic over a wide band of frequencies comprising a pair of metal conductive antenna structures I, 2 in the form of horns connected to a two-conductor transmission line TL. Horns I, 2 comprise, for the major portions of their lengths adjacent their bases (1. e. large ends) conical surfaces of revolution and for their portions adjacent the transmission line TL tapering surfaces which gradually decrease in dimension until they have the same dimensions as the conductors of the transmission line TL to which they are connected. In effect, we can say that the antenna structures I, 2 are cones distorted from the vertical line AA to form bent horns.

A continuous and gradual change in diameter from the transmission line conductors TL to the outermost ends of the horns I, 2 provides a gradual change in the electromagnetic field configuration from that corresponding to the planar wave emanating from the transmission line TL tion has a substantially constant surge impedance throughout its length. In a wave guide for a spherical wave, it is important that, to obtain a constant surge impedance, the conducting surfaces of the wave guide take substantially the shape of conical surfaces of revolution. These conical surfaces of revolution may be composed either of metallic sheet material or a plurality of wires regularly distributed around and lying in a surface of revolution. As for a transmission line where the guided wave is in the form of a plane wave, the surge impedance is constant throughout the length of the line if the ratio conductor--spacing to conductor-diameter is constant. Consequently, to obtain the same constant surge impedance heretofore obtained both in the transmission line and the conical surface of revolution, I gradually increase both the spacing and diameter of the conductors of the line as the guided wave travels from the transmission line to the cone. This gradual increase in dimensions of the transmission line is effected until these dimensions form part and parcel of the conical surfaces of revolution, thus obviating any abrupt changes in dimensions between the transmission line conductors and the cones.

While the foregoing theory believed to be the correct one underlying my invention, it should be distinctly understood that the theoretical explanation is given merely for the purpose of exposition and in order that the invention may be better appreciated. The invention, however, does not depend upon the accuracy of this explanation and is independent of any theory to account for the results achieved.

Fig. 2 illustrates another form of my invention which employs a single hollow cone l, extending outwardly from a reflecting surface 3 which may be the electrically conducting roof of a building, an electrically conducting side wall of a building, or ground. Here the transmission line feeder TL is in the form of a coaxial conductor comprising an inner conductor 4 and an outer conductor 5, both of which are gradually increased in dimension at their upper ends near the apex of the cone I. The inner conductor 4, similarly as in Fig. 1, gradually increases in dimension until it forms part of the cone I'. The outer conductor 5 is curved away from the apex of the antenna I, and also gradually increases in its dimensions so as to form a larger open mouth than would ordinarily be formed if this conductor continued straight upward. It will be apparent, from what has been said before, that the outer conductor 5 expands in dimensions with the ex pansion of the inner conductor 4, so "as to obtain constant ratio of outside to inside diameters of transmission line over some length in order to obtain constant surge impedance.

Fig. 3 illustrates still another arrangement wherein a pair of opposed conductive structures I, 2 of a type substantially similar to that illustrated in Fig. 1, is energized from a pair of coaxial transmission lines TL, TL". These conical structures I, 2, it will be noted, are in the form of horns bent in opposite directions. The outer conductors of the coaxial transmission lines TL", TL" also increase in dimension atthe portions adjacent to the apices of the cones I, 2 so as to form horns in the manner shown in the drawing. Each of these outer conductors of the transmission line increases in diameter with the increase in diameter of the associated inner conductor, so as to provide a substantially constant ratio of outer to inner diameter of. line over some length. It should be noted that the outer conductors of the transmission lines of Fig. 3 extend above the apices of the cones for some appreciable length, and are then flared.

I have found that my antenna and transmission line system, as illustrated in all three figures of-the drawing, give an extremely wide band impedance versus frequency characteristic.

It will be obvious, of course, that the invention is not limited to the precise arrangements illustrated in Figs. 1, 2 and 3, since various modifications may be made Without departing from the spirit and scope of the invention. For example, the conical or horn type of structures shown, illustrated and described in the present specification may be made either of sheet metal or of a cage of wires in the manner very generally shown in my copending application Serial No. 187,594, filed January 29, 1938. 7

What is claimed is: I

1. A short wave antenna and transmission line system havingawide band impedance versus frequency characteristic comprising a pair of conductive structures in the form of oppositely disposed horns, feeder'wires for the smalldimensions of said horns, said feeder wires gradually expanding in diameter and imperceptibly merging with said horns. 1

2. A short wave antenna and transmission line system having a Wide band impedance versus frequency characteristic comprising a single conical surface of revolution extending outward from an electrically conducting surface, a feeder conductor connected to the apex of said surface of revolution, said feeder conductor gradually ex panding in diameter until it merges imperceptibly with said conical surface of revolution.

' PHILIP S. CARTER. 

